My little theory is that while men still made enough money to support good life in the US (50s, 60s) most women just didn't want to work. If you can have a house, nice car, four kids, vacation home, 40 hour week, no credit card debt, no school debt, and all of that on carpenter salary -- why not to enjoy life instead of spending 50-60 hours at the office?
The dirty secret is that most women work because they HAVE TO. It's not a choice. It's sold to the society at large as something glamorous because -- what? They're going to tell the truth? Yeah, you need to work your ass off 50-60 hours a week, with credit card debt, student loan debt, two cars loan, etc, etc. just to be able barely make it to have two kids at 35 ? Because before that you need advanced degree or two. Actually both of you do... I mean how is that a better deal?
I can see that also from the reaction of my wife friends who stayed in the US working to basically help their husbands as one salary won't cut it. It's not like they wouldn't prefer to stay at home with kids. But, again, it's not like they have a choice.